Currently, intense chirped-pulse amplification lasers rely on two distinct types of optical amplifiers: optical parametric amplifiers (OPA) and conventional laser amplifiers. The OPA is superior to the energy-level laser amplification in terms of gain bandwidth; its combination with the chirped-pulse amplification is a promising technology for ultra-high peak power lasers. The exciting outcome is the opportunity to reach high peak powers close to a petawatt and generate few-cycle pulses with tens of millijoules of energy. However, the back-conversion effect, which is encountered in all parametric processes, places a ceiling on the future success of the chirped-pulse OPA scheme. First, the back-conversion effect fundamentally limits the conversion efficiency. Although there have been considerable efforts to mitigate the back-conversion effect in the chirped-pulse OPA, high conversion efficiency close to the theoretical limit (i.e., complete pump depletion) is impossible in principle. To date, a maximum efficiency of 34% has been demonstrated using the intricate technique of spatiotemporal pulse shaping, but conversion efficiencies are typically limited to around 20%. Second, because of the back-conversion effect, OPA devices are highly sensitive to the phase-matching condition and uniformity of the pump intensity. Such OPA characteristics place strict requirement on the pump beam quality and challenge the scalability of the chirped-pulse OPA to higher peak-powers beyond petawatt as the current high-energy lasers are often far from the diffraction limit in the beam-quality.